Split Dataset Example

In this example, we aim to show multiple ways of how you can split your datasets for training, testing, and evaluating your models.

# Authors: Lukas Gemein <l.gemein@gmail.com>
#
# License: BSD (3-clause)

from braindecode.datasets import MOABBDataset
from braindecode.preprocessing import create_windows_from_events

Loading the dataset

Firstly, we create a dataset using the braindecode class <MOABBDataset> to load it fetched from MOABB. In this example, we’re using Dataset 2a from BCI Competition IV.

dataset = MOABBDataset(dataset_name="BNCI2014001", subject_ids=[1])

BNCI2014001 has been renamed to BNCI2014_001. BNCI2014001 will be removed in version 1.1.
The dataset class name 'BNCI2014001' must be an abbreviation of its code 'BNCI2014-001'. See moabb.datasets.base.is_abbrev for more information.

Splitting

By description information

The class <MOABBDataset> has a pandas DataFrame containing additional description of its internal datasets, which can be used to help splitting the data based on recording information, such as subject, session, and run of each trial.

dataset.description

	subject	session	run
0	1	0train	0
1	1	0train	1
2	1	0train	2
3	1	0train	3
4	1	0train	4
5	1	0train	5
6	1	1test	0
7	1	1test	1
8	1	1test	2
9	1	1test	3
10	1	1test	4
11	1	1test	5

Here, we’re splitting the data based on different runs. The method split returns a dictionary with string keys corresponding to unique entries in the description DataFrame column.

splits = dataset.split("run")
print(splits)
splits["4"].description

{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127d090>, '1': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454125a710>, '2': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454125a320>, '3': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454125b100>, '4': <braindecode.datasets.base.BaseConcatDataset object at 0x7f4541258c10>, '5': <braindecode.datasets.base.BaseConcatDataset object at 0x7f4541258580>}

	subject	session	run
0	1	0train	4
1	1	1test	4

By row index

Another way we can split the dataset is based on a list of integers corresponding to rows in the description. In this case, the returned dictionary will have ‘0’ as the only key.

splits = dataset.split([0, 1, 5])
print(splits)
splits["0"].description

{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127c6a0>}

	subject	session	run
0	1	0train	0
1	1	0train	1
2	1	0train	5

However, if we want multiple splits based on indices, we can also define a list containing lists of integers. In this case, the dictionary will have string keys representing the index of the dataset split in the order of the given list of integers.

splits = dataset.split([[0, 1, 5], [2, 3, 4], [6, 7, 8, 9, 10, 11]])
print(splits)
splits["2"].description

{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127cf70>, '1': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127ce80>, '2': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f7c0>}

	subject	session	run
0	1	1test	0
1	1	1test	1
2	1	1test	2
3	1	1test	3
4	1	1test	4
5	1	1test	5

You can also name each split in the output dictionary by specifying the keys of each list of indexes in the input dictionary:

splits = dataset.split(
    {"train": [0, 1, 5], "valid": [2, 3, 4], "test": [6, 7, 8, 9, 10, 11]}
)
print(splits)
splits["test"].description

{'train': <braindecode.datasets.base.BaseConcatDataset object at 0x7f45429de380>, 'valid': <braindecode.datasets.base.BaseConcatDataset object at 0x7f45429de440>, 'test': <braindecode.datasets.base.BaseConcatDataset object at 0x7f4542636b30>}

	subject	session	run
0	1	1test	0
1	1	1test	1
2	1	1test	2
3	1	1test	3
4	1	1test	4
5	1	1test	5

Observation

Similarly, we can split datasets after creating windows using the same methods.

windows = create_windows_from_events(
    dataset, trial_start_offset_samples=0, trial_stop_offset_samples=0)

Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']
Used Annotations descriptions: ['feet', 'left_hand', 'right_hand', 'tongue']

# Splitting by different runs
print("Using description info")
splits = windows.split("run")
print(splits)
print()

# Splitting by row index
print("Splitting by row index")
splits = windows.split([4, 8])
print(splits)
print()

print("Multiple row index split")
splits = windows.split([[4, 8], [5, 9, 11]])
print(splits)
print()

# Specifying output's keys
print("Specifying keys")
splits = windows.split(dict(train=[4, 8], test=[5, 9, 11]))
print(splits)

Using description info
{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f940>, '1': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f7c0>, '2': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127d4e0>, '3': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f340>, '4': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127d090>, '5': <braindecode.datasets.base.BaseConcatDataset object at 0x7f460ab57be0>}

Splitting by row index
{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f4542634d90>}

Multiple row index split
{'0': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f340>, '1': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127d4e0>}

Specifying keys
{'train': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f7c0>, 'test': <braindecode.datasets.base.BaseConcatDataset object at 0x7f454127f940>}

Estimated memory usage: 10 MB